Hydrophilic silicone-organic copolymer elastomers

ABSTRACT

This invention provides compositions which are curable to hydrophilic, water-absorbing silicone-organic copolymer elastomers via free radical polymerization such as by the use of free radical precursors, ultraviolet light or electron beam radiation. The compositions are mixtures of (A) from 50 to 95 parts by weight of block copolymers containing polydiorganosiloxane segments and polyalkyleneoxy segments which block copolymers contain terminal aliphatically unsaturated groups such as those derived from the reaction of isocyanoethyl methacrylate with terminal free hydroxyl groups present on the polyalkyleneoxy segments and the polyalkyleneoxy segments are ultimately attached to the silicon atoms by means of a linkage formed by reaction with a diisocyanate compound and (B) from 5 to 50 parts by weight of at least one substantially water insoluble aliphatically unsaturated organic monomer which is compatible with (A) such as methyl methacrylate. The cured elastomers, some of which are optically clear, are useful as membranes for gas or fluid separations or for the controlled release of bioactive agents such as insecticides, herbicides, or drugs.

BACKGROUND OF THE INVENTION

This application is a divisional of co-pending application U.S. Ser. No.020,216 filed on Mar. 6, 1987, which is a divisional of application U.S.Ser. No. 790,008 filed on Oct. 22, 1986, which is a now abandonedcontinuation-in-part of U.S. Ser. No. 06/683,307, filed on Dec. 18,1984, now abandoned.

This invention relates to compositions which are curable to hydrophilic,water-absorbing silicone-organic copolymer elastomers via free-radicalpolymerization. The hydrophilic elastomers ae useful as membranes forgas and other fluid separations and for the controlled release of drugs.

Polydiorganosiloxane elastomers such as those which are predominantlypolydimethylsiloxanes typically exhibit high permeability to varioustypes of gases as compared with organic elastomers. Polydimethylsiloxaneelastomers generally possess hydrophobic surfaces (i.e., advancingwater-in-air contact angles of greater than about 80° at 25° C. and moretypically in the range of 95°-110°) due to the hydrophobic character ofthe polydimethylsiloxane chains forming the elastomer. As a result oftheir hydrophobic character, such elastomers tend to permit non-polarfluids and compounds to pass more readily through the elastomer thanpolar fluid such as water. It would be desirable to obtain an elastomerwhich possessed some of the high permeability characteristics ofsilicone elastomers, but which is hydrophilic and water-absorbing innature, so as to more readily allow polar materials such as water,alcohols and polar bioactive agents such as hydrophilic drugs,insecticides or herbicides to pass through the elastomer. Thehydrophilic character such as water-in-air contact angle and waterabsorbancy should be modifiable so as to enable one to adjust the rateat which a particular compound will permeate through the elastomer. Ifthe hydrophilic, water-absorbing elastomer is to be used as a membranefor fluid separation, the elastomer should retain as much as possible ofits original unhydrated physical properties such as tensile strength,elongation and tear strength after being hydrated and allowed to absorbwater.

Attempts to provide such elastomers have been made in the past,particularly in the field of eye contact lenses where an oxygenpermeable, soft, hydrophilic elastomeric material is desirable. U.S.Pat. No. 4,136,250 to Mueller, et al. (issued 1/23/79) provides awater-insoluble hydrophilic gel comprising about 20 to 90% by weight of(1) a hydrophilic (a) polymer of identical or different water-solublemonoolefinic monomers or (b) copolymer of said water-soluble monomerswith 1 to 80% (of total monomers) of water insoluble, identical ordifferent monoolefinic monomers; ingredient (1) is cross-linked with (2)about 10 to 80% by weight of a terminal polyolefinic siloxane macromerhaving a molecular weight of from about 400 to about 8500 to form a gel.Unlike the curable composition and hydrophilic elastomers of the presentinvention, Mueller, et al. teach that the siloxane macromer is thehydrophobic portion of the gel product and provides flexible cross-linksand improved oxygen permeability. A water soluble monoolefinic monomeris required to be present as at least 20% by weight of the totalmonoolefinic monomers used to form the Mueller, et al. hydrogel. As willbe described, it was found that the polysiloxane component of certaincompositions can act as the hydrophilic portion within certain limitsand therefore substantially water insoluble aliphatically unsaturatedmonomers can be used to the exclusion of water soluble monoolefinicmonomers to obtain hydrophilic, water-absorbing silicone elastomerswhich are oxygen permeable.

European Patent Publication EP 0 109 355 Al to Mueller, et al,(published June 6, 1983) is similar to the Mueller, et al. '250 Patentabove, but places emphasis on the production of hardpolysiloxane/organic free-radical polymerized copolymes for use ascontact lenses. However, the '355 patent states that soft elastomerswhich are water absorbing can also be made using silicone polyetherblock copolymers as shown in Example 71. The polysiloxane component(8-70% of the copolymer) contains terminal olefinic radicals such asmethacrylate radicals which are bonded to the polysiloxane via adiisocyanate or triisocyanate compound such as isophorone diisocyanate.The polysiloxane may contain polyalkyleneoxy radicals between theorganosiloxy units and the terminal olefinic radicals. The organicmonomer component (92-30%) can be composed of monolefinic monomers,diolefinic monomers or mixtures thereof of which, unlike the '250patent, 85 to 100% of the total monomers are water insoluble monomerssuch as methyl methacrylate. The '355 Publication fails to teach thehereinafter described, elastomeric, water-swellable compositions of thepresent invention which differ in polysiloxane block copolymer structurefrom those of the '355 Publication.

U.S. Pat. No. 4,235,985 to Tanaka, et al. (issued 11/25/80) teachescopolymers for contact lenses which are a copolymer of an organosiloxanemonomer which contains a pendant hydroxyl radical for hydrophilicity andmay optionally contain a polyether group (to improve the hydrophilicityof the copolymer) and a hydrophobic methacrylic acid alkyl ester. Thecopolymer is said to be hydrophilic, but is hard and is substantiallynon-water absorptive unlike the water-absorbing elastomers of thepresent invention. The organosiloxane monomer is employed to provideboth oxygen permeability and hydrophilicity (via the polyether segment),but differs in structure from those employed in the present invention.

U.S. Pat. No. 4,260,725 to Keogh, et al. (issued 4/7/81) teaches awater-absorbing, soft, hydrophilic, flexible contact lens which isoxygen permeable. It teaches a copolymer of organic monomers which mayor may not have hydrophilic groups such as hydroxyl groups presenttherein with a polysiloxane which is alpha, omega-terminally bondedthrough divalent hydrocarbon groups to polymerizably activatedunsaturated groups and which polysiloxane has hydrophilic sidechains.Keogh, et al. fails to teach the polysiloxanes employed in the presentinvention. When polyether sidechains are used to Keogh, et al., theyprefer methoxy end-capped polyether sidechains. This differs from thealiphatically unsaturated terminal groups employed in the presentinvention which enable the entire polysiloxane block copolymer to formthe elastomer and thereby contribute to the retention of physicalproperties after absorbing water. Furthermore, Keogh, et al. make nodistinction between the use of water soluble monomers such as2-hydroxyethylmethacrylate versus substantially water insoluble organiccomonomers such as methyl methacrylate in their compositions while thepresent invention employs substantially water insoluble organicmonomers. These latter monomers are employed in the present invention toobtain cured elastomers with desirable physical strength and resistanceto tearing after absorption of water.

SUMMARY OF THE INVENTION

It is one object of this invention to provide a composition curable to ahydrophilic (i.e., advancing water-in-air contact angle of no greaterthan 80°-85° and more preferably less than 80° at 25° C. after hydrationafter being cured against a polytetrafluoroethylene substrate)silicone-organic copolymer which is capable of absorbing at least 3% byweight of water based upon the total dry weight of the elastomer. Thecomposition is composed of from 50 to 95 parts by weight of apolydiorganosiloxane polyether block copolymer and from 5 to 50 parts byweight of one or more substantially water insoluble aliphaticallyunsaturated organic monomers. The block copolymer portion provides gaspermeability, flexibility and hydrophilicity while the organic portionderived from the unsaturated monomer provides improved physicalproperties before and after hydration. When polyether blocks are pendantfrom a silicon atom present in the polydiorganosiloxane segment of theblock copolymer, the terminal end is capped with an aliphaticallyunsaturated radical for copolymerization with the organic monomer. Thisresults in a copolymer wherein all of the hydrophilic polyether segmentsare tied into the copolymer network thus contributing to the elastomericproperties of the copolymer in addition to serving to render thecopolymer hydrophilic and water absorbing.

It is another object of this invention to provide a hydrophilic, waterabsorbing silicone-organic copolymer elastomer which is permeable anduseful as a membrane for gas and fluid separations. It is also an objectof this invention to provide hydrophilic elastomers which are capable ofreleasing materials such as bioactive agents (e.g., hydrophilic drugs,insecticides and herbicides) at a controlled rate. The release rate canbe controlled by the choice of polysiloxane and polyether segments tovary the hydrophilic character of the copolymer elastomer.

This invention provides improved compositions over the compositionsdescribed in two U.S. patent applications to Chi-long Lee and Wen-BinShyu entitled "Hydrophilic Silicone-Organic Copolymers" (U.S. Ser. No.06/683,308, now U.S. Pat. No. 4,600,751) and "Aqueous EmulsionsContaining Hydrophilic Silicone-Organic Copolymers" (U.S. Ser. No.06/683,303, now U.S. Pat. No. 4,584,337) which were filed on Dec. 18,1984 and assigned to the same assignee as is the present invention.Because of the difference in polysiloxane block copolymer structure fromthe Lee and Shyu compositions, the compositions of the present inventionwere found to have higher tensile strengths for a given level of methylmethacrylate organic monomer and to be essentially non-cytopathic aswill be further described, infra, and may find use in contact with thebody such as for use in the controlled delivery of hydrophilic drugs.The Lee and Shyu compositions tested were found to elicit a cytopathicresponse in testing and are best used for non-body contact purposes.

DETAILED DESCRIPTION OF THE INVENTION

These and other objects of the present invention are provided by acomposition curable to a hydrophilic, water absorbing silicone-organiccopolymer elastomer consisting essentially of

(A) from 50 to 95 parts by weight of a block copolymer of the formula##STR1## wherein

Z is CH₂ ═CR"COOR'"NHCO--, ##STR2##

Q is a divalent radical obtained by removing the NCO radicals from adiisocyanate selected from the group consisting of aliphatic,cycloaliphatic and aromatic diisocyanates,

T is a divalent radical selected from the group consisting of --NR"--and --O-- wherein said T is attached to a carbon atom on --C_(c) H_(2c)-- which is at least the third carbon atom away from the silicon atom towhich the --C_(c) H_(2c) radical is attached,

a is an integer of from 4 to 49, inclusive,

b is an integer of from 0 to 15, inclusive,

c is an integer having a value of 3 or 4,

d is an integer of from 0 to 25, inclusive,

e is an integer of from 5 to 50 inclusive,

d+e is no greater than 50 and e is greater than or equal to d,

f is 0 or 1,

f' is 0 or 1,

f+f'+b is at least 2,

R is a monovalent hydrocarbon or halohydrocarbon radical of from 1 to 6inclusive carbon atoms which is free of aliphatic unsaturation,

R' is a methyl or a phenyl radical,

R" is an alkyl radical of from 1 to 4 inclusive carbon atoms orhydrogen, and

R'" is a divalent hydrocarbon radical of from 2 to 6 inclusive carbonatoms, and

(B) from 5 to 50 parts by weight of at least one substantially waterinsoluble aliphatically unsaturated organic monomer which is compatiblewith said (A), wherein upon curing said composition, an elastomer isobtained which is hydrophilic and capable of absorbing at least 3% byweight of water based upon the total weight of said elastomer beforeexposure to water.

This invention also relates to the copolymer elastomers obtained uponcuring such compositions and to membranes formed from such copolymerelastomers.

The silicone block copolymers employed in the present invention arepreferably produced by first preparing an isocyanate-functionalintermediate by reacting a diisocyanate with a polysiloxane of theformula (I): ##STR3## where T is --NR"-- or --O-- and the remainingsymbols and subscripts are defined above. Preferably, T is --NR"-- and,more preferably, c is 4, --C_(c) H_(2c) -- is --CH₂ CH(CH₃)CH₂ --, andR" is a methyl radical. Such polysiloxanes are known as can be seen froman examination of U.S. Pat. Nos. 2,924,588 (issued Feb. 9, 1960) and3,146,250 (issued Aug. 25, 1964), each to Speier.

Any of a number of well-known aliphatic, cycloaliphatic and aromaticdiisocyanates can be employed to form such a prepolymer. Examples ofdiisocyanates are aliphatic diisocyanates such as tetramethylenediisocyanate and hexamethylene diisocyanate, cycloaliphatic isocyanatessuch as isophorone diisocyanate, cyclohexyl-1,4-diisocyanate, anddicyclohexylmethane-4,4'-diisocyanate and aromatic diisocyanates such asdiphenylmethane-4,4'-diisocyanate. Thus, Q as used in the above formulawould be --(CH₂)₆ -- for hexamethylene diisocyanate and --C₆ H₄ CH₂ C₆H₄ -- for diphenylmethane-4,4'-diisocyanate. When the cured copolymersof the present invention are intended for use in medical applicationssuch as the controlled release of drugs, it is preferred to employdiisocyanates such as dicyclohexylmethane-4,4'-diisocyanate anddiphenylmethane-4,4'-diisocyanate which result in a cured copolymerwhich, as shown in the following examples, does not elicit a significantdegree of cytopathic response in tissue culture or other appropriatetesting for bodily contact applications.

The isocyanato-functional prepolymer is prepared under anhydrousconditions in a conventional manner by reacting the above polysiloxne(I) with an amount of the diisocyanate which is preferably thestoichiometric amount needed to completely react with the --OH or ═NHradicals present in the polysiloxane (I). A slight excess may be used ifsome of the reactants contain small amounts of water which may use upsome of the isocynate radicals. The reaction must be conducted in thepresence of an inert solvent such as anhyrous toluene or tetrahydrofuran(toluene is preferred) when T is --NR"-- to reduce the solids content ofthe mixture and to thereby avoid gelation of the mixture. The reactioncan be accelerated by heating the mixture to from 50°-100° C. for 1-4hours. A catalytic amount of a known condensation catalyst such as anamine (e.g., triethylamine) or a tin catalyst (e.g.,dibutyltindilaurate) can also be used to speed up the reaction of theisocyanate radicals with --OH radicals (amine radicals are normallysufficiently reactive with the isocyanate radicals so that no catalystis typically needed). The free iocyanate content can be monitored bystandard titration methods to determine when the formation of theisocyanate-functional prepolymer product is completed. The reaction isprefrably conducted under mild conditions (e.g., room temperature toabout 50° C.) when the polysiloxane contains primary amino radicals.

The second step is the reaction of a polyether (polyalkyleneoxy) glycolof the average formula H(OCH(CH₃)CH₂)_(d) (OCH₂ CH₂)_(e) OH (d and e aredefined above) with the isocyanate-functional prepolymer productprepared above to produce a polysiloxane polyether block copolymerprepolymer which contains .tbd.COH radicals. Polyether glycols of thistype are commercially available materials which are sold by, forexample, BASF Wyandotte Corporation, Parsippany, NJ 07054 and The DowChemical Company, Midland, MI 48640. Examples of such polyether glycolsare HO(CH₂ CH₂ O)_(e) H where e has an average value of about 5, 13 and50 and polyols of the formula HO(CH₂ CH₂ O)_(e) (CH(CH₃)CH₂ O)_(d) Hwhere d and e both have an average of about 24. To prepare thepolysiloxane polyether block copolymer perpolymers, a sufficient amountof the desired polyether polyol is added to the isocyanate-functionalprepolymer to provide the stoichiometric amount of polyether polyolneeded to react one of the two .tbd.COH radicals present in that polyolwith the isocyanate radicals present in the isocyanate-functionalprepolymer. A slight excess of polyol may be used to insure that all ofthe isocyanate radicals are removed to avoid possible cytopathic effectsin the cured product caused by such radicals. The reaction is conductedunder anhydrous conditions in the presence of a inert solvent as notedabove and a catalytic amount of a condensation catalyst such asdibutyltindilaurate (0.00005% tin based on the total amount ofpolyalkylene glycol was used with good results) if a catalyst was notadded when the prepolymer was prepared. The formation of thepolysiloxane polyether block copolymer prepolymer is preferablyconducted by heating the reactants at 50°-100° C. for 1-2 hours.Reaction is continued until the free isocyanate content of the blockcopolymer prepolymer is substantially nil. It is recognized that it ispossible that both hydroxyl radicals of the polyether polyol can reactwith isocyanate radicals to form chain-extended polysiloxane polyetherblock copolymer prepolymers, but it is believed that the amount of sucha reaction will be small. Such chain-extended polymers should contributeto the wettability and water absorptivity of the cured elastomericsilicone/organic copolymers of the present invention and will notdetract greatly from the desired properties of the cured elastomers ofthe present invention.

The third step used to prepare the terminally aliphatically unsaturatedblock copolymers employed in the present invention for reaction with thehereinafter described organic monomers is one which preferably involvesreacting the polysiloxane polyether block copolymer prepolymers madeabove which are substantially composed of prepolymers of the formula##STR4## with, preferably, a stoichiometric amount of aliphaticallyunsaturated isocyanate-functional compound of the formula CH₂ ═CR"COOR'"NCO to produce a block copolymer wherein R" can be methyl, ethyl,propyl, butyl or hydrogen and is preferably a methyl radical and R'" isan alkylene radical of from 2 to 6 inclusive carbon atoms such asethylene, propylene, butylene and hexylene with ethylene beingpreferred. Examples of aliphatically unsaturated compounds useful forreaction with the prepolymers are isocyanatoethyl methacrylate andisocyanatoethyl acrylate (CH₂ ═CHCOO(CH₂)₂ NCO). The isocyanatecompounds provide a one step addition to the block copolymer prepolymersunder mild reaction conditions in the presence of a catalyst such as anorganotin catalyst or an amine without generating by-products. 0.3% oftriethylamine based upon the total amount of block copolymer prepolymerand isocyanate compound was found to work well with the above blockcopolymer prepolymers and isocyanatoethyl methacrylate. Most preferredis isocyanotoethyl methacrylate. Since the acrylate radicals arereactive, a small amount of an inhibitor such as hydroquinone (0.00003%based on the amount of aliphatically unsaturated isocyanate-functionalcompound) must be added along with the catalyst to prevent prematurereaction with the acrylate radicals. After the reaction with theisocyanate-functional compound is complete, the solvent is preferablystripped at relatively low temperature (e.g. less than 50° C.) undervacuum conditions from the product to obtain a silicone polyether blockcopolymer useful in the present invention. Use of infrared spectrograms(i.e., follow loss of isocyanate peak) of reaction mixtures or otherknown techniques such as titration methods to determine when eachreaction involving isocyanates is complete is preferred. It is wellknown that block copolymers are typically a mixture of block copolymersof varying chain lengths having the previously described structure. Theoverall block copolymer composition is typically described as onewherein the average chain length of segments such as polyethyleneoxyunits in the block copolymer composition is referred to by an integersuch as "e is an integer from 5 to 50" in the foregoing formula. Theblock copolymers of the present invention also contain substitutedsiloxy units (designated by the subscripts "a" and "b" which may be indiscrete blocks of, e.g., several (RR'SiO) units or may contain (RR'SiO)units interspersed with ##STR5## units along the same linearpolysiloxane chain.

As can be seen from the foregoing formulas, each R can be a hydrocarbonor a halohydrocarbon radical from 1 to 6 inclusive carbon atoms which isfree of aliphatic unsaturation such as methyl, ethyl, propyl, hexyl,cyclohexyl, chloromethyl, 3,3,3-trifluoropropyl or 1,1,1-trifluorohexylradicals. Preferably R is selected from the group consisting of methyl,phenyl and 3,3,3-trifluoropropyl radicals. For highest permeability togases such as oxygen, R and R' are most preferably methyl radicals.

To obtain a hydrophylic, water-absorbing silicone-organic copolymerelastomer, the block copolymer must contain a sufficient amount ofhydrophilic ether (alkyleneoxy) units to overcome the hydrophiliccharacter contributed by the polysiloxane segments and by the organicpolymer segments derived from the unsaturated monomers. A polysiloxanesegment consisting of about 50 siloxy units which does not containhydrophilic polyether segments is about the maximum which can be presentand still obtain a hydrophilic surface having an advancing water-in-aircontact angle of no greater than about 80°-85° at 25° C. when moldedagainst polytetrafluoroethylene. This is particularly true when theblock copolymer contains only two terminal polyether chains which is apreferred block copolymer (i.e., b=0). To obtain the best elastomericproperties, it is preferred that a block copolymer be employed wherein ais an integer of from 8 to 14 inclusive, and e is an integer of from 10to 15 inclusive. Since the ethyleneoxy --OCH₂ CH₂ -- unit is morehydrophilic than the propyleneoxy ##STR6## unit, the ratio of theseunits in the chain can be varied to modify the hydrophilicity and waterabsorption of the elastomer. If more than one half of the alkyleneoxyunits present in the polyether segment are propyleneoxy units, thehydrophilicity of the elastomer may be compromised. For this reason, itis best that d be no greater than 25 and that the value of e be greaterthan or equal to d. Preferably, d=0 and the hydrophilicity and waterabsorption of the elastomer is varied by controlling the number andratio of ethyleneoxy units to RR'SiO units in the polydiorganosiloxanesegments. The polyether segments should not consist of more than 50alkyleneoxy units, (i.e., the sum of d+e should be no greater than 50).

The permeability of the elastomer can also be controlled by varying thenumber and ratio of alkyleneoxy units to RR'SiO units. Block copolymerswherein b has a value of greater than 2 will tend to form more tightlycross-linked, less elastomeric copolymers than block copolymers whereinf+f'+b=2. It is best to minimize the amount of block copolymers whereinf+f'+b is greater than 2 in the composition to obtain the bestelastomeric properties, particularly elongation values. The gaspermeability of the cured elastomer begins to rapidly decrease for agiven ratio of block copolymer to organic monomer as the siloxane unitcontent of the block copolymer is decreased. 50 parts of block copolymerper 100 parts total block copolymer and organic monomer appears to beabout the minimum necessary to retain a reasonable amount of gaspermeability. When the block copolymer content of the elastomer isincreased to about 95 parts, the physical properties of the curedelastomer tend to become poor. The water absorption of the elastomershould be at least 3% by weight of water based upon the total weight ofthe dry cured elastomer before exposure to water. The water absorptionof the cured elastomer will be dependent upon the polyalkyleneoxycontent of the block copolymer. An increase in polyalkyleneoxy contentof the block will generally increase the water absorption of the curedelastomer for a given ratio of block copolymer and organic monomer.

The block copolymers employed in the present invention differ from thematerials described in the aforementioned Lee and Shyu patentapplications and from the aforementioned Mueller, et al. U.S. Patent andEuropean Patent Application because of their structure. When T is--NR"--, there is one urea and at least two urethane linkages betweenthe silicon atom and the terminal acrylate- or methacrylate-functionalradical. When T is --O--, there are at least three urethane linkagesbetween the silicon atom and the terminal acrylate- ormethacrylate-functional radical. The terminal acrylate or methacrylateradical is isocyanate-functional and therefore reacts directly with the═COH present in the block copolymer prepolymer and therefore avoids thenecessity for the preparation of another isocyanate-functionalprepolymer after a hydroxyl radical terminated block copolymer isprepared. In such a case, Mueller, et al. would require a diisocyanateto link a material such as a hydroxy-functional acrylate (e.g.,2-hydroxyethyl methacrylate) with .tbd.COH radicals on the blockcopolymer to provide terminal methacrylate-functional radicals.Furthermore, the Mueller, et al. patent and patent publication do notteach use of a linkage formed by a diisocyanate between the silicon atomand the polyalkyleneoxy polyether block attached to the silicon atom. Itis this linkage which also differentiates the block copolymers used inthe compositions of the present invention from those described in theaforementioned Lee and Shyu patent applications. By preparing the blockcopolymers in this manner rather than using the platinum-catalyzedaddition of an allyl radical terminated polyalkyleneoxy alcohol (e.g.,CH₂ ═CHCH₂ (OCH₂ CH₂)_(e) OH where e is 12-14) to .tbd.SiH described inthe Lee and Shyu patent applications, it was found that the curedelastomeric products of the present invention were substantially free ofcytopathic response in the tissue culture test described in thefollowing examples. It was also found that the cured hydrophilicelastomeric products of the present invention generally possessed highertensile strengths than similar copolymers of the Lee and Shyu type andstill retained at least one-third and generally approximately one halfof their original tensile strength after absorbing water.

The block copolymers are copolymerized with from 5 to 50 parts by weightof at least one substantially water insoluble aliphatically unsaturatedorganic monomer which is compatible with the block copolymer. The term"compatible" is intended to mean that the block copolymer and organicmonomer are sufficiently miscible and free radical polymerizable witheach other that they are capable of forming a substantially cross-linkedcopolymer rather than being substantially a mixture of two homopolymers.A copolymer provides better physical properties. By "substantially waterinsoluble", it is meant that the monomer does not contain free hydroxylradicals, polyalkyleneoxy radicals, carboxyl radicals, amine radicals orother radicals which by themselves or as salts render the monomer watersoluble. Examples of water soluble monomers are2-hydroxyethylmetharcrylate and N-vinyl pyrrolidone. Examples ofmonomers which are substantially water insoluble include the hydrocarbonesters of acrylic and methacrylate acid such as methyl acrylate, methylmethacrylate, ethyl acrylate, butyl acrylate and cyclohexylmethacrylate, styrene, alphamethylstyrene, para-methylstyrene, vinylacetate, vinyl propionate, allyl ether, and acrylonitrile. Preferably,such monomers are of the formula ##STR7## wherein W is selected from thegroup consisting of --COOR"", --OOCCH₃ and --C₆ H₅ wherein R"" is analkyl radical of from 1 to 6 inclusive carbon atoms such as methylmethacrylate, methyl acrylate, vinyl acetate and styrene. Methylmethacrylate is preferred. When higher tensile strength and tearresistant hydrophilic elastomers are desired such as for use as forexample, membranes, it is preferable that from 30 to 50 parts by weightof the total weight of block copolymers and substantially waterinsoluble aliphatically unsaturated organic monomers present in thecomposition be such organic monomers. When higher levels of organicmonomer (e.g. about 50% monomer based on the total amount of acrylate ormethacrylate terminated block copolymer and monomer) are employed, thecompositions tend to have low viscosities and are more difficult to moldin thin films.

The block copolymer and organic monomers are homogeneously blendedtogether to form a composition which is then cured to a hydrophilicelastomer by exposing the composition to free radical polymerizationconditions. Thus, the compositions can be cured by exposing them toheat, ultraviolet radiation, electron beam radiation, or other forms ofionizing radiation. If ultraviolet radiation is employed, it can bedesirable to include an effective amount of a photoinitiator such asbenzophenone with or without a promoter such as an amine such asdimethyl aniline in the composition before curing.

Free radical polymerization can also be inititated by further includingfrom 0.1 to 10 parts by weight of a free radical initiator per 100 partsby weight of block copolymers and organic monomers in the composition.0.36 parts of 2,2-azo-bis-isobutyronitrile initiator per 100 parts ofblock copolymer and organic monomer was found to work well as shown inExamples 4-6. The composition containing a free radical initiator canthen be cured by heating the composition to a temperature which issufficient to initiate production of free radicals or else simply byquickly adding the free radical initiator if it produces free radicalsat room temperature. Examples of useful free radical initiators areperoxides such as 2,5-bis-(t-butylperoxy)-2,5-dimethyl hexane,tert-butyl peroxy-2-ethylhexanoate (also known as "tert-butylperoctoate"), benzoyl peroxide, methyl ethyl ketone peroxide and azocompounds such as 2,2-azo-bis-isobutyronitrile and2,2'-azo-bis-(2,4-dimethylvaleronitrile). Because the organic monomerstend to be volatile, it is best to at least initially cure thecompositions at temperatures which are no greater than about 200° C.,and preferably no greater than 100° C., and under conditions which tendto inhibit escape of the unreacted monomer such as in a closed mold.Post curing at higher temperatures may be accomplished after the initialcure since most of the volatile organic monomers should have beencopolymerized in the initial curing step. Heat/press cures at 60° C. for15 minutes and then 15 minutes at 100° C. followed by a postcure at 80°C. for at least 12 hours produced acceptable cured elastomers(2,2-azo-bis-isobutyronitrile was used as a catalyst) as shown in thefollowing Examples.

Nonreactive solvents can be added to reduce the viscosity of thecompositions, but it is best to rely on the organic monomers to reducethe viscosity of the compositions. Aqueous emulsions formed from thecurable compositions of the present invention can be prepared by addingsuitable emulsifiers to the compositions. Emulsions can be prepared inthe same manner as is described in the U.S. patent application entitled"Aqueous Emulsions Containing Hydrophilic Silicone-Organic Copolymers"(U.S. Ser. No. 06/683,303, now U.S. Pat. No. 4,584,337) filed on Dec.18, 1984 in the names of Chi-long Lee and Wen-Bin Shyu and assigned tothe same assignee as is the present invention.

The term "consisting essentially of" as used in this Specification andthe accompanying claims is intended to mean that the combination ofblock copolymers and substantially water insoluble organic polymers toprovide hydrophilic, water-absorbing silicone-organic copolymerelastomers forms the basis for the present invention. If desired, otheradditional ingredients which do not affect the hydrophilic, waterabsorbing character of the cured elastomers can be added to theaforementioned compositions. Examples of such additional ingredients canbe silica and other fillers, fiber reinforcement, antioxidants,pigments, dyes and colorants and the like.

Because the permeability and the water absorption of the curedelastomers can be varied, the cured elastomers are suitable asselectively permeable membranes useful, for example, in gas or fluidseparations such as in separating oxygen from nitrogen or for alteringthe ratio of water to methanol in water/methanol mixtures. Likewise,bioactive agents such as insecticides, larvicides, acaricides andherbicides or fertilizers could be incorporated within the curablecompositions of the present invention and the compositions can then becured to form hydrophilic, water absorptive elastomers capable ofreleasing the agents included therein over a period of time which isdependent upon the composition of the elastomer. After conductingappropriate safety and efficacy testing for the compositions selected,cured elastomers of the present invention may find use in applicationsinvolving contact with the human body such as for the controlleddelivery of drugs by incorporating the drug into the compositions of thepresent invention and curing the mixture or by using a membrane of thecured elastomer to control delivery of the drug from a reservoir. Someof the elastomers were optically clear after hydration and can find usein applications where transparent elastomers are required such ascoatings for glass or for fabric treatments.

In the following Examples, the advancing water-in-air contact angleswere measured using a sessile drop method at room temperature (about21±2° C.) on dry (unhydrated) samples of the cured elastomer using adistilled water drop. The elastomer was molded against TEFLON®polytetrafluoroethylene film in a molding chase. The measurement wascompleted within about 5-10 minutes from the application of the waterdrop to the elastomer. The instrument used was a NRL Contact AngleGoniometer, Model No. A-100 which is a product of Rame-Hart, Inc.,Mountain Lake, N.J. The contact angles were also measured using CH₂ I₂.

The percent water absorption of the cured elastomer products wasmeasured by molding a slab of cured elastomer product (weight about 1 g,thickness 0.03 or 0.06 inches). The dry slab was then either totallyimmersed in distilled water or placed in a dessicator above, but not inphysical contact with, a saturated sodium bisulfate solution to providea 50% relative humidity atmosphere at room temperature for the period oftime described in the following examples. The percent water absorptionreported was calculated as follows: ##EQU1## where W_(H) is the weightof the slab after hydration and W_(U) is the dry (unhydrated) weight ofthe slab.

The physical properties of the cured elastomers were measured onunhydrated and hydrated samples as indicated in the Examples using thefollowing ASTM Methods: ASTM D412--ultimate tensile strength (tensilestress) and elongation at break; ASTM D624--tear (Die B) and ASTMD2240--durometer (Shore A). The physical properties reported are theaverage properties of at least 3 samples.

The permeability of water vapor through an approximately 30 mil (0.76mm) thick dry (unhydrated) membrane formed of the cured elastomerproducts reported in the Examples was determined at room temperatureaccording to the procedure described in ASTM D-1653 using a PaynePermeability Cup, purchased from Fisher Scientific Co, 711 ForbesAvenue, Pittsburgh, PA 15219. The wate vapor permeability was calculatedfrom the loss of water through the cured elastomer membrane at roomtemperature. The liquid being measured was placed in the bottom of thePayne Permeability Cup and was not in actual contact with the membranebeing tested. In the Examples, P_(H).sbsb.2_(O) is permeability to watervapor in units of ##EQU2##

The following Examples are illustrative only and should not be construedas limiting the invention which is properly delineated in the appendedclaims.

Unless otherwise mentioned, all parts and percentages relating tocompositions are by weight.

EXAMPLES 1-3

An amino-functional polydimethylsiloxane of the general formula

    MeNHCH.sub.2 CH(Me)CH.sub.2 SiMe.sub.2 (OSiMe.sub.2).sub.a CH.sub.2 CH(Me)CH.sub.2 NHMe

was prepared where "Me" in this and the following Examples is a methylradical. This material (hereinafter "Polymer A") was made byequilibration of a mixture of low molecular weightpolydimethylcyclosiloxane predominantly composed ofoctamethylcyclotetrasiloxane and ##STR8## in the presence of water and asmall amount of potassium hydroxide catalyst and had an amine equivalent(by titration with perchloric acid in acetic acid using a Methyl Violetindicator) of 684 which corresponds to a number average molecular weightfor the amino-functional polysiloxane of about 2×684 or 1368. Thus, a inthe above formula would have an average value of about 15.4.

76.5 milliliters (81.8 g) of dicyclohexylmethane-4,4'-diisocyanate (0.62molar equivalents of isocyanate radicals) and 300 ml of anhydroustoluene was added to a dried (moisture-free) 3 liter, 3-necked,round-bottomed flask equipped with an additional funnel, air-poweredstirrer, a air-cooled condenser, a temperature controller forcontrolling a heating mantle and a dry nitrogen source to maintain theinterior of the flask under a nitrogen atmosphere. The flask was filledwith nitrogen gas before addition of the diisocyanate solution. Thestirrer was started and a solution of 212 g of Polymer A (0.31 molarequivalents of ═NH radicals) in 800 ml of anhydrous toluene was added tothe contents of the flask via the addition funnel over about a 15 minuteperiod. 380.4 g of a dry solution of a polyoxyethylene glycol(hereinafter "Polyol A") having a number average molecular weight ofabout 600 (Polyglycol E600 from The Dow Chemical Company, Midland, Mich.48640) in toluene (calculated to contain 210 g of Polyol A whichcorresponded to about 0.62 molar equivalents of .tbd.COH radicals) and0.2 mol of a 10 percent (weight/weight solution of dibutyltindilauratein dry toluene was then added to the contents of the flask. The additionfunnel was washed with 200 ml of dry toluene which was allowed to enterthe flask. The stirring contents of the flask were heated to 100° C. andheld at 100° C. for 1 hour. The heating mantle was shut off and thecontents of the flask were allowed to stir without any further heatingovernight.

The next day, 50 milligrams of hydroquinone and 1.8 g of triethylaminewere stirred into the contents of the flask. With the stirring on andthe contents of the flask under a nitrogen blanket, 96.1 g ofisocyanatoethylmethacrylate (0.62 molar equivalents of isocyanateradicals) was added to the contents of the flask through the additionfunnel and the funnel was then washed with 118 ml of dry toluene whichwas allowed to drop into the contents of the flask. The contents of theflask were allowed to stir for 1 hour at room temperature and was thenheated to and kept at 50° C. for 3 hours. The toluene was then strippedfrom the contents of the flask under vacuum at 30° C. for 16 hours togive a theoretical yield of 600 g of a glassy silicone block copolymer("Silicone Block Copolymer A") substantially having the average formula##STR9## where Z is CH₂ ═C(Me)COOCH₂ CH₂ NHC(O)--, E is --(OCH₂ CH₂)_(e)0-- where e has an average value of about 13, ##STR10## T is --N(Me)--and a has an average value of about 15.

To produce the composition of Example 1, 66.7 g of methylmethacrylatemonomer was added to the contents of the flask and stirred untilhomogeneous. 275 g of this solution was removed from the flask as thecomposition of Example 1 which was intended to contain 90% SiliconeBlock Copolymer A and 10% methylmethacrylate monomer.

The composition of Example 2 was made by adding 48.9 g ofmethylmethacrylate monomer to the material remaining in the flask andstirring until homogeneous. 275 g of the contents of the flask wereremoved from the flask as the composition of Example 2 which wasintended to contain 80% Silicone Block Copolymer A and 20%methylmethacrylate monomer.

Finally, 98.9 g of methylmethacrylate monomer was added to the materialremaining in the flask and it was stirred until homogeneous. Thecontents of the flask contained the composition of Example 3 which wasintended to contain 50% Silicone Block Copolymer A and 50%methylmethacrylate monomer.

It was later discovered that a calculation error had been made and twicethe stoichiometric amount of isocyanatoethylmethacrylate was used inpreparing Examples 1-3. The excess isocyanotoethylmethacrylate was notthought to be removed during stripping and was thought to coreact withthe methylmethacrylate and Polymer A during cure of each composition.Therefore, the composition of Example 1 was believed to contain about 7weight percent of coreacted isocyanotoethylmethacrylate in addition tothe other two ingredients. Similarly Examples 2 and 3 were believed tocontain about 6 and 4 weight percent, respectively, of coreactedisocyanotoethylmethacrylate in addition to the other two ingredients.Examples 8-10 were prepared to show the use of a stoichiometric amountof isocyanotoethylmethacrylate.

2.0 g of a free radical curing catalyst, 2,2-azo-bis-isobutyronitrile,was added to each composition and mixed 30 minutes by rolling a bottleof each sample for 30 minutes. The catalyst readily dissolved in Example3, but was not completely dissolved in Example 1 even after severaldays. The excess catalyst in Example 1 was allowed to settle to thebottom overnight and the composition above the settled solids was usedto make cured elastomers the next day.

All molded samples made from the catalyzed compositions of Examples 1-3were prepared by curing each catalyzed composition in a molding chaseunder about 20,000 p.s.i. of pressure for 15 minutes at 60° C. (toreduce loss of volatile monomer) followed by 15 minutes at 100° C.Example 3 was somewhat difficult to mold because the viscosity of themixture was low. The molded samples were then postcured in an oven for aminimum of 12 hours at 80° C. The cured samples were then devolatilizeda minimum of 2 hours in a vacuum oven at 80° C. and 1 Torr pressure toremove any volatiles such as unreacted organic monomer. It was notedthat the molded elastomer samples turned yellow if the oven temperatureexceeded 100° C. Examples 1 and 2 resulted in visually optically clearelastomers while those of Example 3 were clear, but had a bluish tint.

The physical properties obtained on dry (0% relative humidity,anhydrous) samples and those obtained after soaking cured samples indistilled water for 5 days at room temperature are reported in Table I.The advancing water-in-air and CH₂ I₂ -in-air contact angles of thecured elastomers (dry) is also reported in Table I. The percent waterabsorption of each cured dry sample was measured in two ways: by anincrease in sample weight (a) after a 24 hour immersion in distilledwater and (b) after 24 hours at 50% relative humidity (stored in adessicator above, but not in contact with, a saturated solution ofsodium bisulfate), both at room temperature. Finally, the water vaporpermeability measured on a membrane of each cured composition isreported in Table I.

EXAMPLES 4-6

The compositions of Examples 4-6 were made in a manner similar to thatused in Examples 1-3, but an aromatic diisocyanate was used in thepreparation of the silicone block copolymer.

Thus, 77.5 g of diphenylmethane-4,4'-diisocyanate (0.62 molarequivalents of isocyanate radicals) was dissolved in 500 ml of drytoluene under a nitrogen blanket in a flask of the type used in Examples1-3. The contents of the flask had to be heated to 50° C. to dissolvethe diisocyanate. The heating mantle was shut off and 212 g of Polymer A(0.31 equivalents of ═NH radicals) was dissolved in 600 ml of drytoluene, placed in the addition funnel and added to the stirringcontents of the flask dropwise over a period of about 1.5 hours. Thecontents of the flask were not externally heated during this addition.When this addition was complete, 380.4 g of the same solution ofpolyethyleneoxy glycol/toluene solution used in Examples 1-3 was addedto the addition funnel and was then rapidly added to the stirringcontents of the flask. The addition funnel was washed with 100 ml of drytoluene which was then added to the contents of the flask. The contentsof the flask were heated to 100° C., held at that temperature for 1hour, and then cooled to room temperature.

Then 50 milligrams of hydroquinone and 1.8 g of triethylamine were addedto the stirring contents of the flask followed by 96.1 g ofisocyanatoethylmethacrylate. Finally, 200 microliters of a 10% by weightsolution of dibutyltindilaurate in dry toluene was added to the contentsof the flask and the contents were allowed to stir overnight at roomtemperature to complete production of the silicone block copolymer.

The next day, the toluene was stripped from the contents of the flaskunder vacuum conditions (about 1 Torr) at 35°-40° C. for 6 hours (untilno more bubbles formed). The theoretical weight of the material in theflask was 595.6 g. The silicone block copolymer in the flask ("SiliconeBlock Copolymer B") substantially had the average formula: ##STR11##where Z is CH₂ ═C(Me)COOCH₂ CH₂ NHC(O)--, E is --(OCH₂ CH₂)_(e) O--where e has an average value of about 13, Q is --C₆ H₄ --CH₂ --C₆ H₄ --,T is --N(Me)-- and a has an average value of about 15.4.

The composition of Example 4 was made by adding 66.2 g ofmethylmethacrylate monomer to the contents of the flask and stirringuntil homogeneous. 274 g of the contents were withdrawn as thecomposition of Example 4 which was intended to contain 90% SiliconeBlock Copolymer B and 10% methylmethacrylate monomer.

The composition of Example 5 was made by adding 48.5 g ofmethylmethacrylate monomers to the material remaining in the flask andstirring until homogeneous. 274 g of the contents of the flask wereremoved as the composition of Example 5 which was intended to contain80% Silicone Block Copolymer B and 20% methylmethacrylate monomer.

Finally, 97.4 g of methylmethacrylate monomer was added to the materialremaining in the flask and it was stirred until homogeneous. Thecontents of the flask contained the composition of Example 6 which wasintended to contain 50% of Silicone Block Copolymer B and 50% ofmethylmethacrylate monomer.

It was later discovered that a calculation error had been made and twicethe stoichiometric amount of isocyanatoethylmethacrylate was used inpreparing Examples 4-6. The excess isocyanotoethylmethacrylate was notthought to be removed during stripping and was thought to coreact withthe methylmethacrylate and Polymer A during cure of each composition.Therefore, the composition of Example 4 was believed to contain about 7weight percent of coreacted isocyanotoethylmethacrylate in addition tothe other two ingredients. Similarly Examples 5 and 6 were believed tocontain about 6 and 4 weight percent, respectively, of coreactedisocyanotoethylmethacrylate in addition to the other two ingredients.

Since 2 g of 2,2-azo-bis-isobutyronitrile catalyst was not completelysoluble in Example 1, only 1 g of that catalyst was added to eachcomposition of Example 4-6 and each sample was allowed to standovernight at room temperature to permit the catalyst to dissolve. Curedelastomers were prepared from the catalyzed compositions in the samemanner as was described for Examples 1-3. The same tests were run on thecured elastomers Examples 4-6 as for Examples 1-3 and the results arereported in Table I.

Referring to Table I, the cured compositions were stiff elastomers(durometer of 78-92) which exhibited relatively high dry tensile andtear strengths at break when dry. Tensile strength increased markedlywhen the level of methylmethacrylate was increased. Except for Example 5which retained 30% of its original tensile strength after beinghydrated, the remaining cured elastomers retained between 40-63% oftheir dry tensile strength value. Tear strengths for the dry sampleswere also very good. The cured samples also retained at least 40% oftheir original dry elongation at break value.

The advancing water-in-air contact angle of the dry samples all showedthat they were hydrophilic (contact angle of less than 80°) andgenerally tended to become lower the longer the water droplet wasallowed to stand on the surface of the sample. The advancing CH₂ I₂-in-air contact angle (a polar compound) decreased with increasingmethylmethacrylate content for Examples 1-3, but was not consistent forExamples 4-6. These contact angles generally followed the trends set bythe water contact angles observed.

The water absorption of the cured samples decreased with increasingmethylmethacrylate content as did the permeability of the sample towater (P_(H).sbsb.2_(O)). The cured compositions of Examples 2 and 5were hydrophilic materials which had a good balance of tensile (dry andhydrated) and tear strength coupled with 19% and 15% water absorptionand relatively good permeation to water vapor, a polar compound. It isexpected that one way which the permeability of the cured compositionsto other polar compounds could be altered is by varying the ratio of thesilicone block copolymer to methylmethacrylate used in the compositionsemployed in these Examples.

The cured compositions of Examples 1-6 were tested, in vitro, by placingduplicate samples of the cured elastomer and extracts from the curedelastomer in direct contact with a confluent monolayer of humanembryonic foreskin cells (type HR 218) and each was incubated at 37° ina humidified 5% carbon dioxide atmosphere for 24 hours. After incubationfor 24 hours, the cytopathic effect of the direct contact samples andtheir extracts were each microscopically evaluated against both apositive and a negative control. No cytopathic effect was deemed to beproduced by the materials tested or their extracts. It was noted thatone of the two samples of the cured composition of Example 6 produced avery slight cytopathic response. This level was deemed to be a marginalresponse: because neither the other sample in direct contact nor the twoextracts for this sample exhibited a response, the test was deemed to bepassed (i.e., no cytopathic effect in this test). The Lee and Shyu curedelastomer mentioned, (See Example 8 of "Hydrophilic Silicone-OrganicCopolymer Elastomers" to Lee, et al.) exhibited a cytopathic effect inthis type of test. These materials appear to show promise for use inapplications involving contact with the body after further appropriatetesting confirms the results of this screening testing.

                                      TABLE I                                     __________________________________________________________________________                                     Advancing                                                                              Water Absorption                    Dry Samples, 0% R.H..sup.1                                                                           Hydrated Samples.sup.6                                                                  Contact Angle (°)                                                               24 hours, Wt. %                     Ex. #                                                                             Tensile.sup.2                                                                      Elong..sup.3                                                                       Durom..sup.4                                                                       Tear.sup.5                                                                        Tensile.sup.2                                                                      Elong..sup.3                                                                       H.sub.2 O                                                                         CH.sub.2 I.sub.2                                                                   IMMERS..sup.7                                                                       50% R.H..sup.1                                                                      .sup.P H.sub.2                                                                O.sup.8                 __________________________________________________________________________    1   620/ 46   78   37/ 390/ 20   67  67   22.0  1.5   12.9                        4.27           6.5 2.69                                                   2   1500/                                                                              60   82   130/                                                                              610/ 28   65  64   18.6  1.3   10.4                        10.34          22.8                                                                              4.21                                                   3   3430/                                                                              38   90   260/                                                                              2170/                                                                              47   68  58   7.2   0.8   2.4                         23.65          45.5                                                                              15.0                                                   4   810/ 45   79   52/ 350  26   70  50   17.8  1.4   9.5                         5.58           9.1 2.41                                                   5   1890/                                                                              61   88   150/                                                                              570/ 41   73  61   14.9  1.1   6.2                         13.0           26.3                                                                              3.93                                                   6   3820/                                                                              61   92   610/                                                                              1830/                                                                              47   64  52   5.0   0.6   2.1                         26.3           106.8                                                                             12.6                                                   __________________________________________________________________________     .sup.1 R.H. = Relative Humidity                                               .sup.2 Tensile strength at break in p.s.i./megapascals (MPa)                  .sup.3 Elongation at break in %                                               .sup.4 Shore A durometer value in points.                                     .sup.5 Tear strength, die B, in pounds per linear inch                        (p.l.i.)/kilonewtons per meter (KN/m) where 1,000 p.l.i. = 175 kN/m.          .sup.6 Immersed in distilled water for 5 days at room temperature before      testing.                                                                      .sup.7 Immersed in distilled water for 24 hours at room temperature befor     testing.                                                                      .sup.8 Water vapor permeability in units of (mg H.sub.2 O) (mm)/(cm.sup.2     (24 hr).                                                                 

EXAMPLE 7

An amino-functional polydimethylsiloxane was made in manner similar tothat of polymer A to obtain "Polymer B" which had an amine equivalent(by titration with perchloric acid in acetic acid using a Methyl Violetindicator) of 681 which corresponds to a number average molecular weightof about 2×681 or 1362. This polymer was derivitized with aceticanhydride and stripped at 110° C. (1 Torr pressure) overnight. Thestripped product was found to have a number average molecular weight of1315 via a gel permeation chromatographic method.

To prepare a silicone block copolymer, 8 g ofdiphenylmethane-4,4'-diisocyanate (0.064 molar equivalents of isocyanateradicals) were added to a flask under a nitrogen gas blanket as inExamples 1-3 along with 62.5 ml of tetrahydrofuran solvent. 20 g ofPolymer B (0.0294 molar equivalents of ═NH radicals) was dissolved inanother 62.5 ml of tetrahydrofuran and the solution was added to theaddition funnel. The solution was added to the stirring contents of theflask over about a 15 minute period of time at 25° C. After 30 minutes,the contents of the flask was clear. Then 23.4 g (0.070 molar equivalentof .tbd.COH) of the same polyethylenoxy glycol (neat) used in Examples1-6 was added to the contents of the flask and the contents became hazy.23 microliters of a 10% solution of dibutyltindilaurate indiethyleneglycol diethylether was added to the stirring contents of theflask and the contents were heated to 50°-55° C. and held at thattemperature for 2 hours. Then, 3 milligrams of hydroquinone (dissolvedin tetrahydrofuran solvent) was added to the contents of the flaskfollowed by 8.6 g (0.057 molar equivalents of isocyanate radicals--a55.7% molar equivalent excess) of isocyanatoethylmethacrylate. The useof an inhibitor such as hydroquinone (to prevent premature reaction ofthe methacrylate radicals) was necessary because a batch made in amanner similar to this one gelled three hours after addition of theisocyanotoethylmethacrylate was made. The isocyanotoethylmethacrylatewas allowed to react for 2 hours at 50°-55° C.

To render any remaining isocyanate radicals inactive, 2.2 g (0.03 moles)of n-butylamine was added to the contents of the flask and allowed toreact for 20 minutes at 50°-55° C. The tetrahydrofuran and any excessvolatile materials such as n-butylamine was stripped from the contentsof the flask under full vacuum (about 1 Torr pressure) at 25° C. toobtain a white pasty silicone block polymer ("Silicone Block CopolymerC"). In this Example, Silicone Block Copolymer C was prepared throughthe use of molar excesses of diisocyanate, polyol and monoisocyanate. Itis an alternative, but currently less preferred, procedure.

Then, 30 g of methylmethacrylate monomomer was added to the SiliconeBlock Copolymer C in the flask and stirred well to form a whitedispersion to which 0.8 g of 2,2-azo-bis-isobutyronitrile was added. Thecontents of the flask were stirred well and deaired (to remove airbubbles) by subjecting the contents of the flask to a vacuum (about 1Torr pressure) for 10-20 minutes. The catalyzed composition was storedin a refrigerator until portions of it were cured into 10-20 mil(0.254-0.508 mm) thick membranes between two polytetrafluoroethylenerelease sheets and into test slabs for physical property and toxicologytesting the next day. The portions were heat-press cured (about 15,000p.s.i. pressure) at 70°-90° C. for 30 minutes. Before curing, thecomposition contained a ratio 67 parts of Silicone Block Copolymer C to33 parts methylmethacrylate monomer along with the excessisocyanatoethylmethacrylate/n-butylamine reaction product.

The dry (unhydrated) cured elastomer of this Example 7 had a tensilestrength 1570 p.s.i. (10.8 MPa) and an elongation at break of 200%.After 7 days immersion in distilled water at room temperature, the curedelastomer had a tensile strength of 1,000 p.s.i. (6.9 MPa) and thusretained about 64% of its original tensile strength after beinghydrated.

Samples of the cured elastomer of Example 7 were tested, in vitro, forcytopathic effect (direct contact and extract) as described for Examples1-6. In direct contact (after extraction) the cured elastomer was ratedas having no cytopathic effect. The extract from the cured elastomer wasrated as having a cytopathic effect. In view of the testing results inExamples 4-6, it was thought that a contaminant such as n-butylamine orexcess isocyanate compound might have accounted for this result. Thus,the procedure of Examples 4-6 is preferred when materials free fromcytopathic effects are desired. Extraction to remove unwantedby-products may also be desirable.

EXAMPLES 8-10

Since an excess of isocyanatoethylmethacrylate was used Examples 1-6 andthe excess isocyanate radicals were not removed by reaction withn-butylamine as in Example 7, Examples 8-10 were run to demonstrate theuse of a stoichiometric amount of isocyanatoethylmethacrylate and thusessentially repeated Examples 1-3. It was thought that the presence ofthe excess isocyanatoethylmethacrylate in Examples 1-6 might result inthe formation of a hydrophilic radical when the free isocyanate radicalswere exposed to atmospheric moisture or when the cured elastomer wasplaced in water and thus alter the water absorption and/orhydrophilicity of the samples.

An amino-functional polydimethylsiloxane was made in the same generalmanner as Polymer A of Example 1 to produce "Polymer C" which had anamine equivalent of 577 which corresponds to a number average molecularweight of 2×577 or 1154 (i.e., the average value of the subscript "a" inthe formula is about 12.5). Polymer C thus contained a lower amount ofhydrophobic polydimethylsiloxane content than did Polymer A.

"Silicone Block Copolymer D" was prepared in the same general manner asSilicone Block Copolymer A by adding 106 g ofdicyclohexylmethane-4,4'-diisocyanate (0.795 molar equivalents ofisocyanate radicals) to a dried 2 liter flask of the type used and asequipped in Examples 1-3 containing a dry nitrogen gas atmosphere. Thestirrer was started and a solution of 230 g of Polymer C (0.398 molarequivalents of ═NH radicals) in 465 g dry toluene was added to thecontents of the flask via an addition funnel over a 10 minute period oftime. 457 g of a dry solution of Polyol A in toluene (calculated tocontain 0.795 molar equivalents of .tbd.COH radicals) and 200microliters of solution of 10% dibutyltindilaurate in toluene was thenadded to the stirring contents of the flask. The stirring contents ofthe flask was heated to 100° C. for 2 hours. After heating, the contentsof the flask were cooled to 50° C. and 61.7 g ofisocyanatoethylmethacrylate (0.398 molar equivalents of isocyanateradicals) was added to the stirring contents of the flask along with 2 gof triethylamine catalyst and 1 g hydroquinone. The contents weremaintained at 50° C. until an infrared spectrogram of the contentsshowed that the isocyanate peak had essentially disappeared indicatingthat the reaction of the isocyanatoethylmethacrylate with thecarbinol-functional prepolymer was essentially complete. Upon completionof the reaction, the contents of the flask were stripped under vacuum toremove the volatile toluene to obtain a silicone block copolymer of thesame average formula shown for Silicone Block Copolymer A where Z, E, Qand T were the same as for Silicone Block Copolymer A and "a" had anaverage value of about 12.5 (hereinafter "Silicone Block Copolymer D").

Example 8 (10% methylmethacrylate monomer, 90% Silicone Block CopolymerD), Example 9 (20% methylmethacrylate monomer, 80% Silicone BlockCopolymer D) and Example 10 (50% methylmethacrylate monomer, 50%Silicone Block Copolymer D) were made by dilution of Silicone BlockCopolymer D with methylmethacrylate monomer. To facilitate incorporationof the free-radical curing catalyst into the compositions of eachExample, a sufficient amount of 2,2-azo-bis-isobutyronitrile was addedto the methylmethacrylate used to prepare each Example to provide 0.2 gof 2,2-azo-bis-isobutyronitrile per 100 g of total methylmethacrylateand Silicone Block Copolymer D present.

All molded samples made from the catalyzed compositions of Examples 8-10were prepared by curing each catalyzed composition in a molding chaseunder about 20,000 p.s.i. of pressure for 15 minutes at 50° C. (toreduce loss of volatile monomer) followed by 15 minutes at 100° C. Themolded samples were then postcured in an oven for about 16 hours at 80°C. in a vacuum oven at 5 Torr pressure.

The results of the testing of the molded elastomer samples are reportedin Table II. Examples 8 and 9 were generally lower in tensile strength,durometer and tear strength than Examples 1 and 2 and higher inelongation value, water absorption and permeability to water vapor.Example 10 produced a cured elastomer which was lower in tensilestrength than Example 3, but was higher in elongation, durometer, tearvalues, water absorption and water vapor permeability. The advancingwater-in-air contact angles for Examples 8 and 10 were comparable toExamples 1 and 3 while Example 9 had a much higher water-in-air contactangle than did Example 2 even though the water absorption of the curedelastomer of Example 9 was twice that for Example 2. This material wouldbe considered as being hydrophilic in view of the water absorptioncharacteristics.

Samples of each cured elastomer of Examples 8-10 were tested, in vitro,for cytopathic effect (direct contact and extract) as described forExamples 1-6. In direct contact, each cured elastomer was rated ashaving no cytopathic effect. Extracts from each cured elastomer usingcottonseed oil were rated as having no cytopathic effect. The MinimumEssential Medium (i.e., the growth medium for the cells) extract fromthe cured elastomer of Example 10 was rated as having no cytopathiceffect while the cured elastomers from Examples 8 and 9 were rated ashaving a cytopathic effect. The Minimum Essential Medium Extract test (avery sensitive test) was again run on the cured elastomers of Examples 8and 9; the results were that Example 8 was rated as having a cytopathiceffect and Example 9 was rated as having no cytopathic effect.

The same cured sample of Example 8 (previously tested twice) wassubmitted a third time for direct contact and Minimum Essential Mediumextract testing along with two other samples of Example 8 one of whichwas made by curing the composition of Example 8 again for the sameperiod of time as the above sample, and to make the other, a differentsample of methylmethacrylate was added to Silicone Block Copolymer D andthat composition was cured as above. All three samples were rated ashaving a cytopathic effect in the Minimum Essential Medium extract. Itappears that some unknown material was being extracted and was causing aresponse; the identity of this material was not determined. All three ofthese samples were rated as having a cytopathic effect in direct contactwith the cell layer. This was unexpected since none of the curedelastomers tested exhibited such a response when tested in directcontact, particularly the previous two samples of the cured elastomer ofExample 8. No explanation for these results was readily apparent,especially in view of the results of the previous testing. It appearsthat further appropriate, conventional testing beyond this screeningtesting is warranted before such materials are used in contact with thebody.

                                      TABLE II                                    __________________________________________________________________________                                     Advancing                                                                              Water Absorption                    Dry Samples, 0% R.H..sup.1                                                                           Hydrated Samples.sup.6                                                                  Contact Angle (°)                                                               24 hours, Wt. %                     Ex. #                                                                             Tensile.sup.2                                                                      Elong..sup.3                                                                       Durom..sup.4                                                                       Tear.sup.5                                                                        Tensile.sup.2                                                                      Elong..sup.3                                                                       H.sub.2 O                                                                         CH.sub.2 I.sub.2                                                                   IMMERS..sup.7                                                                       50% R.H..sup.1                                                                      .sup.P H.sub.2                                                                O.sup.8                 __________________________________________________________________________    8   170  58   64   15  200  33   68  60   33    1.6   37.3                    9   360  100  75   29  300  60   83  47   28    2.0   20.1                    10  3267 105  93   346 1774 100  66  56   14    2.0   6.4                     __________________________________________________________________________     .sup.1 R.H. = Relative Humidity                                               .sup.2 Tensile strength at break in p.s.i.                                    .sup.3 Elongation at break in %                                               .sup.4 Shore A durometer value in points.                                     .sup.5 Tear strength, die B, in pounds per linear inch                        (p.l.i.)/kilonewtons per meter (KN/m) where 1,000 p.l.i. = 175 kN/m.          .sup.6 Immersed in distilled water for 5 days at room temperature before      testing.                                                                      .sup.7 Immersed in distilled water for 24 hours at room temperature befor     testing.                                                                      .sup.8 Water vapor permeability in units of (mg H.sub.2 O) (mm)/(cm.sup.2     (24 hr).                                                                 

EXAMPLES 11-25

In these Examples, a number of silicone block copolymers substantiallyhaving the average formula ##STR12## where Z is CH₂ ═C(Me)COOCH₂ CH₂NHC(O)--, E is --(OCH₂ CH₂)_(e) O--, ##STR13## T is --N(Me)-- were madeaccording to the general procedure described in Examples 8-10 usingamino-functional polydimethylsiloxanes, polyethylene glycols andisocyanatoethylmethyacrylate as reactants as described in those Examplesto produce silicone block copolymers having the average values of "e"and "a" in the formula above which are described below. The siliconeblock copolymers were mixed with various amounts of methylmethacrylatemonomer, catalyzed with 2,2-azo-bis-isobutyronitrile and cured asdescribed for Examples 8-10. The silicone block copolymers themselveswere also catalyzed and cured in the same manner to form curedelastomers. The physical properties of the cured elastomers wereevaluated and the results are reported in Table III. The normalizedintrinsic release rate of progesterone and testosterone from certain ofthese cured elastomers was measured at 37° C. (body temperature) and adiffusion coefficient for each elastomer/hormone drug combination testedalong with the drug solubility in the polymer was calculated. Theseresults are reported in Table IV.

Example 11 was a silicone block copolymer of the above average formulawhich was prepared in the same manner as was Silicone Block Copolymer Dusing an amino-functional polydimethylsiloxane of the type shown at thebeginning of the text for Examples 1-3 (amine equivalent of 577). Thevalues of "e" and "a" in the above silicone block copolymer formula wereexpected to be close to that for Silicone Block Copolymer D. The numberaverage molecular weight of Example 11 was determined to be 5100 and theweight average molecular weight was determined to be 14,000 using aconventional gel permeation chromatographic method using conventionalpolystyrene reference samples. Methylmethacrylate monomer was added tothe polymer of Example 11 to produce compositions having the followingamounts of methylmethacrylate ("MMA") and the polymer of Example 11("Ex. 11") by weight: Example 12-15% MMA, 85% Ex. 11; Example 13-30%MMA, 70% Ex. 11; Example 14-45% MMA; 55% Ex. 11. The cured elastomer ofExample 14 was observed to have a rather high advancing water-in-aircontact angle although it absorbed 13.2% by weight of water indicatingthat it was hydrophilic.

Example 15 was a silicone block copolymer of the above average formulawhich was prepared in the same manner as Silicone Block Copolymer Dusing stoichiometric amounts of reactants. Example 15 was prepared usingan amino-functional polysiloxane of the type shown at the beginning ofthe text for Examples 1-3 (amine equivalent of 583), but thepolyoxyethylene glycol used was one which had a nominal number averagemolecular weight of about 1,000. Thus, referring to the silicone blockcopolymer formula above, the silicone block copolymer of Example 15 hada calculated value of "e" of about 22 and a calculated value of "a" ofabout 12-13. The number average molecular weight of Example 15 wasdetermined to be 5000 and the weight average molecular weight wasdetermined to be 12,000 using a conventional gel permeationchromatographic method using conventional polystyrene reference samples.Methylmethacrylate monomer was added to the polymer of Example 15 toproduce compositions having the following amounts of methylmethacrylate("MMA") and the polymer of Example 15 ("Ex. 15") by weight: Example16-22.5% MMA, 77.5% Ex. 15; and Example 17-45% MMA, 55% Ex. 15.

Example 18 was a silicone block copolymer of the above average formulawhich was prepared in the same manner as Silicone Block Copolymer Dusing stoichiometric amounts of reactants. Example 18 was prepared usingan amino-functional polysiloxane of the type shown at the beginning ofthe text for Examples 1-3 (amine equivalent of 677), but thepolyoxyethylene glycol used was one which had a nominal number averagemolecular weight of about 1,450. Thus, referring to the silicone blockcopolymer formula above, the silicone block copolymer of Example 18 hada calculated value of "e" of about 32-33 and a calculated value of "a"of about 15. The number average molecular weight of Example 18 wasdetermined to be 4,600 and the weight average molecular weight wasdetermined to be 11,000 using a conventional gel permeationchromatographic method using conventional polystyrene reference samples.Methylmethacrylate monomer was added to the polymer of Example 18 toproduce a composition (Example 19) having 22.5% methylmethacrylate and77.5% of the polymer of Example 18.

Example 20 was a silicone block copolymer of the above average formulawhich was prepared in the same manner as Silicone Block Copolymer Dusing stoichiometric amounts of reactants. Example 20 was prepared usingan amino-functional polysiloxane of the type shown at the beginning ofthe text for Examples 1-3 having about three times thepolydimethylsiloxane content of Silicone Block Copolymer D (amineequivalent of 1653), and the polyoxyethylene glycol used was one whichhad a nominal number average molecular weight of about 600. Thus, in thesilicone block copolymer formula above, the silicone block copolymer ofExample 20 had a calculated value of "e" of about 13 and a calculatedvalue of "a" of about 41-42. The number of average molecular weight ofExample 20 was determined to be 6,200 and the weight average molecularweight was determined to be 27,000 using a conventional gel permeationchromatographic method using conventional polystyrene reference samples.Methylmethacrylate monomer was added to the polymer of Example 20 toproduce compositions having the following amounts of methylmethacrylate("MMA") and the polymer of Example 20 ("Ex. 20") by weight: Example21-15% MMA, 85% Ex. 20; Example 22-30% MMA, 70% Ex. 20; Example 23-45%MMA; 55% Ex. 20.

Example 24 was a silicone block copolymer of the above average formulawhich was prepared in the same manner as Silicone Block Copolymer Dusing stoichiometric amounts of reactants. Example 24 was prepared usingan amino-functional polysiloxane of the type shown at the beginning ofthe text for Examples 1-3 which contained about three times thedimethylpolysiloxane content of Silicone Block Copolymer D (amineequivalent of 1646), and the polyoxyethylene glycol used was one whichhad a nominal number average molecular weight of about 1,450. Thus, inthe silicone block copolymer formula above, the silicone block copolymerof Example 24 had a calculated value of "e" of about 32-33 and acalculated value of "a" of about 41. The number average molecular weightof Example 24 was determined to be 10,000 and the weight averagemolecular weight was determined to be 45,000 using a conventional gelpermeation chromatographic method using conventional polystyrenereference samples. Methylmethacrylate monomer was added to the polymerof Example 24 to produce a composition (Example 25) having 45%methylmethacrylate and 55% of the polymer of Example 24.

Table III illustrates the effect of varying the amounts ofpolydimethylsiloxane content, polyoxyethylene content and monomercontent on the physical properties of the copolymers of the presentinvention. Generally, increasing the amount of monomer improved thetensile strength of the cured elastomers while the permeability to watervapor and water absorption decreased. Examples 20-23 (highestpolydimethylsiloxane content and lowest polyoxyethylene content tested)tended to have advancing water-in-air contact angles in the 80-85 degreerange even though the cured elastomers absorbed a significant amount ofwater.

Table IV describes the results of the testing of nominal 0.020 inch(0.05 centimeter) membranes of the cured elastomers made from thecompositions shown in Table IV for permeability to testosterone andprogesterone. A conventional Ghannom-Chien membrane permeation apparatuswas used to carry out this testing according to the procedure describedby K. Tojo, Y. Sun, M. Ghannom, and Y. W. Chien in "Characterization ofa Membrane Permeation System For Controlled Drug Delivery Studies",AIChE Journal, vol. 31, no. 5, pages 741-746, May, 1985. TheGhannom-Chien apparatus contains two temperature-controlled cellsequipped with stirrers. The two cells are separated by the membrane tobe tested. One cell is filled with a solution containing the drug to beevaluated and the other cell is filled with a neat solution and is thereceiving cell for the drug which has permeated through the membrane.The testing was done at a cell temperature of 37° C. using a stir rateof 425 r.p.m. The solution used was 40/60 volume/volume solution ofpolyethylene glycol having a nominal molecular weight of 400/distilledwater. The slope of the total concentration of the hormone drug presentin the receiving cell versus time adjusted by a normalizing factor basedon the cell dimensions was multiplied by the normalized membranethickness to obtain the normalized intrinsic Release Rate inmicrograms/centimeter * seconds ("Release Rate") reported in Table IV.The data obtained by spectrometrically monitoring the increase inconcentration of hormone drug in the receiving cell versus time was usedto calculate the Diffusion Coefficient in square centimeters/secondreported in Table IV. The quotient of the Release Rate divided by theDiffusion Coefficient gives a relative measure of the Drug Solubility(in micrograms per cubic centimeter) of the drug in the cured elastomer.A sample of a peroxide-vulcanized silicone elastomer was also includedin the testing as a comparative Example of the permeationcharacteristics of progesterone and testosterone through apolydimethylsiloxane elastomer which is a hydrophobic elastomer which isessentially non-water absorbent.

The results shown in Table IV indicate that increasing the amount ofpolyoxyethylene content in the silicone block copolymer resulted in anincreased Release Rate of testosterone as shown for Examples 11, 15 and18. Increasing the amount of polydimethylsiloxane content resulted in adecrease in Release Rate of testosterone as shown for Examples 11 and21. Permeability to testosterone and progesterone generally decreasedwith increasing amounts of methylmethacrylate content. The diffusioncoefficients generally followed the same trends with the exception ofExamples 15-17. For Examples 15 and 17, the values for progesteroneappeared to follow the same trends. The Drug Solubility values for thecured elastomers of the present invention were typically much higherthan those observed for the control polydimethylsiloxane elastomer. TheExamples show that, for a specific drug, the Release Rate and theDiffusion Coefficient for the cured elastomers of the present inventioncan be varied by changing the polydimethylsiloxane content and/or thepolyoxyethylene content of the silicone block copolymers of the presentinvention and/or by changing the amount of methylmethacrylate used tomake the cured elastomer.

                                      TABLE III                                   __________________________________________________________________________    Dry Samples, 0% R.H..sup.1                                                                          Hydrated Samples.sup.6                                                                 Advancing                                                                              Water Absorption                      Ten-                  Ten-     Contact Angle (°)                                                               24 hours, Wt. %                       Ex. #                                                                             sile.sup.2                                                                        Elong..sup.3                                                                       Durom..sup.4                                                                       Tear.sup.5                                                                        sile.sup.2                                                                        Elong..sup.3                                                                       H.sub.2 O                                                                         CH.sub.2 I.sub.2                                                                   IMMERS..sup.7                                                                        50% R.H..sup.1                                                                      .sup.P H.sub.2                                                                O.sup.8                                                                           % MMA.sup.9          __________________________________________________________________________                                                             2                    11  300 32   70   16.5                                                                              240 21   75  69   35.6   1.78  22.7                                                                              0                    12  280 48   67   55  180 28   78  48   32.5   1.72  12.6                                                                              15                   13  1700                                                                              102  93   157 680 68   77  61   23.5   0.94  10.8                                                                              30                   14  3500                                                                              76   95   347 1580                                                                              72   87  60   13.2   1.0   4.72                                                                              45                   15  230 46   60   9   190 27   74  46   79.9   7.5   38.2                                                                              0                    16  320 77   75   25  340 45   74  46   56.8   2.0   24.1                                                                              22.5                 17  3020                                                                              130  93   401 1300                                                                              57   77  56   30.2   1.2   13.4                                                                              45                   18   44 53   61   8    0  0    75  68   104    2.2   46.7                                                                              0                    19  209 57   65   6   133 33   75  64   73     2.0   74.5                                                                              22.5                 20  150 34   55   6    90 18   85  62   22.1   1.39  9.58                                                                              0                    21  290 71   65   23  180 42   83  50   16.5   0.98  7.59                                                                              15                   22  1450                                                                              104  89   116 670 87   80  51   9.92   0.70  3.85                                                                              30                   23  1020                                                                              55   95   110 1420                                                                              66   81  49   6.05   0.60  3.02                                                                              45                   24   72 72   40   41   10 27   70  69   104    --    55.9                                                                              0                    25  159 58   56   14  100 38   70  52   63     --    33.9                                                                              22.5                 __________________________________________________________________________     .sup.1 R.H. = Relative Humidity                                               .sup.2 Tensile strength at break in p.s.i.                                    .sup.3 Elongation at break in %                                               .sup.4 Shore A durometer value in points.                                     .sup.5 Tear strength, die B, in pounds per linear inch                        (p.l.i.)/kilonewtons per meter (kN/m) where 1,000 p.l.i. = 175 kN/m.          .sup.6 Immersed in distilled water for 5 days at room temperature before      testing.                                                                      .sup.7 Immersed in distilled water for 24 hours at room temperature befor     testing.                                                                      .sup. 8 Water vapor permeability in units of (mg H.sub.2 O)                   (mm)/(cm.sup.2) (24 hr).                                                      .sup.9 % MMA = weight percent methylmethacrylate present in total             composition.                                                             

                                      TABLE IV                                    __________________________________________________________________________                            Diffusion                                                              Release Rate                                                                         Coefficient                                                                          Drug Solubility.sup.3                          Example No.                                                                          % MMA.sup.1                                                                         Drug.sup.2                                                                        (mg/cm·sec)                                                                 (cm.sup.2 /sec)                                                                      (mg/cm.sup.3)                                  __________________________________________________________________________    11     0     T   8.02 × 10.sup.-5                                                               8.63 × 10.sup.-9                                                               9,300                                          12     15    T   6.52 × 10.sup.-5                                                               5.04 × 10.sup.-9                                                               12,900                                         13     30    T   9.4 × 10.sup.-6                                                                2.93 × 10.sup.-9                                                               3,200                                          15     0     T   1.94 × 10.sup.-4                                                               3.24 × 10.sup.-8                                                               5,990                                          16     22.5  T   9.75 × 10.sup.-5                                                               8.09 × 10.sup.-9                                                               12,050                                         17     45    T   1.28 × 10.sup.-5                                                               3.11 × 10.sup.-9                                                               4,120                                          15     0     P   1.96 × 10.sup.-4                                                               2.04 × 10.sup.-8                                                               9,610                                          17     45    P   1.60 × 10.sup.-5                                                               1.78 × 10.sup.-9                                                               8,990                                          18     0     T   3.14 × 10.sup.-4                                                               5.13 × 10.sup.-8                                                               6,120                                          19     22.5  T   2.44 × 10.sup.-4                                                               1.02 ×  10.sup.-8                                                              23,920                                         19     22.5  P   1.01 × 10.sup.-4                                                               1.25 × 10.sup.-8                                                               8,080                                          21     15    T   3.78 × 10.sup.-5                                                               5.25 × 10.sup.-9                                                               7,200                                          22     30    T   2.35 × 10.sup.-5                                                               2.87 × 10.sup.-9                                                               8,200                                          24     0     T   2.81 × 10.sup.-4                                                               1.61 × 10.sup.-8                                                               17,450                                         25     22.5  T   1.79 × 10.sup.-4                                                               1.22 × 10.sup.-8                                                               14,670                                         PDMS.sup.4                                                                           0     T   5.55 × 10.sup.-5                                                               6.55 × 10.sup.-7                                                               85                                             PDMS.sup.4                                                                           0     P   5.63 × 10.sup.-4                                                               8.94 × 10.sup.-7                                                               630                                            __________________________________________________________________________     .sup.1 Weight Percent Methylmethacrylate in total composition.                .sup.2 T = testosterone, P = progesterone.                                    .sup.3 Quotient of Release Rate divided by Diffusion Coefficient.             .sup.4 Control sample of a peroxidevulcanized polydimethylsiloxane            elastomer.                                                               

That which is claimed is:
 1. A method of controlling the delivery of abioactive agent to a substrate, comprising the steps of:(a) contactingthe substrate with a membrane formed from a water absorbing, hydrophilicsilicone organic elastomer comprising a polymerization product formedfrom a composition consisting essentially of (A) from 50 to 95 parts byweight of at least one block copolymer of the formula ##STR14## whereinZ is CH₂ ═CR"COOR'"NHCO--, ##STR15## Q is a divalent radical obtained byremoving the NCO radicals from a diisocyanate selected from the groupconsisting of aliphatic, cycloaliphatic and aromatic diisocyanates, T isa divalent radical selected from the group consisting of --NR"-- and--O-- wherein said T is attached to a carbon atom on --C_(c) H_(2c) --which is at least the third carbon atom away from the silicon atom towhich the --C_(c) H_(2c) -- radical is attached, a is an integer of from4 to 49, inclusive, b is an integer of from 0 to 15, inclusive, c is aninteger having a value of 3 or 4, d is an integer of from 0 to 25,inclusive, e is an integer of from 5 to 50 inclusive, d+e is no greaterthan 50 and e is greater than or equal to d, f is 0 or 1, f' is 0 or 1,f+f'+b is at least 2, R is a monovalent hydrocarbon or halohydrocarbonradical of from 1 to 6 inclusive carbon atoms which is free of aliphaticunsaturation, R' is a methyl or a phenyl radical, R" is an alkyl radicalof from 1 to 4 inclusive carbon atoms or hydrogen, and R'" is a divalenthydrocarbon radical of from 2 to 6 inclusive carbon atoms, and (B) from5 to 50 parts by weight of at least one substantially water insolublealiphatically unsaturated organic monomer which is compatible with said(A)cured by maintaining the composition under free radicalpolymerization conditions for a sufficient amount of time to obtain saidpolymerization product, said polymerization product being capable ofabsorbing at least 3% by weight of water based upon the total weight ofsaid polymerization product before exposure to water, and (b) contactingthe membrane with a reservoir of the bioactive agent.
 2. A method asclaimed in claim 1 wherein the bioactive agent is a drug and thesubstrate is a patient's body.
 3. A method as claimed in claim 1,wherein said (B) is at least one monomer of the formula ##STR16##wherein W is selected from the group consisting of --COOR"", --OOCCH₃and --C₆ H₅ wherein R"" is an alkyl radical of from 1 to 6 inclusivecarbon atoms and a is an integer of from 8 to 14, inclusive, d is O, eis an integer of from 10 to 20, inclusive, R is a methyl, phenyl or3,3,3-trifluoropropyl radical, T is --NR""-- and Z is CH₂ ═CR"COO(CH₂)₂NHCO--.
 4. A method as claimed in claim 3, wherein the bioactive agentis a drug and the substrate is a patient's body.
 5. A method as claimedin claim 3, wherein R and R' are each methyl radicals, b is 0, c is 4,R" is --CH₃ and Q is selected from the group consisting of ##STR17## 6.A method as claimed in claim 5, wherein the bioactive agent is a drugand the substrate is a patient's body.